Such valveless pumps with a single rotary piston are used, for example, as metering pumps for fluids in all those cases in which accurately metered amounts must be delivered. Depending on the direction of rotation of the rotary piston, the direction [of delivery] of the pump is reversible. The piston closes itself on the delivery or suction side, so that no shutoff or check valves are needed. The delivery capacity of the pump can be controlled in a particularly simple manner by varying the rotation speed.
In prior-art pumps, the periodic axial movement of the piston is generated by a type of crank mechanism. The crank is fastened to the rotary piston, and the end of the crank is hinged to a cam plate on the drive shaft. Such a mechanism is described, e.g., in U.S. Pat. No. US-A-3,168,872. The cylinder with the rotary piston movable therein is mounted such that the piston axis can be deflected relative to the axis of the drive shaft. As long a the drive shaft and the piston are arranged such that they are coaxial, the piston only rotates in the cylinder and does not perform a stroke. As soon as the piston axis is deflected, the piston is displaced in the cylinder as a consequence of the different planes of rotation of the cam plate and the crank. The desired piston stroke can be set by selecting the degree of deflection of the piston axis relative to the axis of the drive shaft.
One disadvantage of the prior-art pump drive is the fact that the displacing clutches are subject to relatively great mechanical stress and are therefore liable to malfunction. In addition, it is not always possible or desirable for the drive shaft to be put in an oblique position relative to the piston axis.